Adjustable axles have been used for vehicles, particularly axles for agricultural vehicles such as tractors, implements, and the like. Adjustable axles have provided such vehicles with improved versatility to accommodate row spacing and other requirements. Occasionally, these vehicles are driven over public highways, for example, when tractors and implements are transported between farmsteads and fields or when produce is transported from the field directly to a nearby market or storage facility. Many states, however, have statutes which provide that vehicles having an axle width of greater than a specified amount (typically 8 feet) are not avowed to use the highway without special permit. Hence, the agricultural vehicle axle must be capable of complying with such standards. On the other hand, when such vehicles are used during field operation, it is often desirable to have the axle width extended to provide additional stability. This is particularly true when the loads are heavy and the fields or roads are on hill sides. Also, when operation is in growing crops it is desirable to have a vehicle whose axle can be adjusted to allow travel between the rows of the planted field. This is especially important when the crops are tall such as standing corn or grapes in a vineyard.
Farm vehicles having wheels that can be moved to adjust the spacing between the wheels are known in the art. It is desirable to adjust the spacing between wheels of the farm vehicle to match the row spacing of a crop in which the vehicle is being used to minimize damage to the crop.
Some crops, such as those found in vineyards, have extremely narrow rows along banked hillsides. Tractors used for orchard and vineyard cultivating require adjustable wheel spacing to allow fit between rows. Unlike sprayers and other equipment used for row crop farming, it is inconvenient for equipment used for tillage in orchards and vineyards to straddle the rows. Typically, tractors used in vineyards and orchards are small and narrow. When these tractors are driven at higher speed to travel between fields, it is desired that the wheel spacing be increased to provide more stability. A means to quickly adjust wheel spacing would aid the operator in changing between narrow, in field, spacing to wider transport spacing.
A number of means to achieve this quick adjustment of spacing are known in the prior art. However, these applications have been applied to large vehicles which straddle the crops. Because of the height of the crops a narrow tractor to fit between the rows is most desirable. This requires a vehicle with adjustable tire tread widths between 1.15 and 2.15 meters. The conventional use of sliding beams or tubes is not practical due to the length of the support members required.
What is needed is an adjustable axle that allows for a much narrower minimum spacing than the conventional sliding tube techniques allow.